Piano
He liked how the instrument sounds when he touch it.
Moreover, how his sister seems to cheer up when he played a song or two for her and that is why he asked his parents to buy him one on his 10th birthday.
Then he also order one of the Digimon craftsmen to make him one in the digital world to make sure that he can still play for his sister in the other world but she doesn't cheer up when he played it, she cried.
"Rather than torturing all those poor Digimon, why don't we just go home and you play some song for me?" she asked between sob but he didn't listen.
He continue to plot on how to take over the world where his beloved sister can walk and run freely, telling himself that it can cheer her up and it's the best for her while the music instrument lay forgotten in some dark part of the castle.
Later, he realized how stupid it is and thought about how much better if they both had just stayed home where he can played the piano freely and not putting his sister in danger.
He only realized this after they had run away from the castle and only Hideto remain.
A lonely Pianist who lost his reason to play, both his friends and sister already run away to his enemy side.
Neo Saiba regret his decision to use his life to dictate in some monster world and throw away the instrument he used to love so much.
Authors Note : I was inspired by the V-Tamer bios that stated the character hobby. If I had time I will do the other as well except Taichi who never has a bios.
Next probably Rei or Hideto.